Dive Table (Decompression Table)

Dive tables, also known as decompression tables, are essential tools for divers planning and executing underwater excursions. These tables, available as printed cards or booklets, provide vital information to determine a safe decompression schedule for a specific dive profile and breathing gas mixture. Dive tables are integral to preventing decompression sickness, a potentially life-threatening condition caused by rapid changes in ambient pressure.

Historical Background

The development of dive tables traces back to the early 20th century when John Scott Haldane, a British physiologist, conducted pioneering research on the effects of pressure on the human body. Haldane’s work laid the foundation for the creation of the first decompression tables, which were subsequently adopted and refined by navies and diving organizations worldwide.

In the early days, dive tables primarily focused on air as the breathing gas. However, as diving technology advanced and the use of mixed gases such as Nitrox and Trimix became more prevalent, dive tables were adapted to accommodate these new gas mixtures.

Fundamentals of Dive Tables

Dive tables consist of a series of columns and rows that present various dive parameters, including depth, bottom time, and surface interval. The primary function of these tables is to help divers calculate the appropriate decompression stops required during their ascent, based on the accumulated nitrogen in their bodies.

1. Depth: The depth column indicates the maximum depth reached during a dive. Depths are usually listed in feet or meters.
2. Bottom Time: Bottom time refers to the total time spent at depth. Dive tables use this value to determine the appropriate decompression stops needed during the ascent.
3. No-Decompression Limit (NDL): The NDL is the maximum allowable bottom time at a specific depth without requiring decompression stops. Exceeding the NDL necessitates a staged ascent with decompression stops to avoid decompression sickness.
4. Surface Interval: The surface interval is the time spent on the surface between dives. Dive tables use this information to adjust for residual nitrogen levels in the body, which can affect the decompression schedule for subsequent dives.
5. Repetitive Dive Groups: This parameter categorizes divers based on residual nitrogen levels following a dive. Dive tables use these groups to account for the cumulative effects of multiple dives and adjust decompression requirements accordingly.

Dive Table Methodology

Dive tables are based on mathematical models and empirical data that simulate the uptake and release of nitrogen in body tissues during a dive. The tables represent a conservative approach, offering a margin of safety to account for individual variations in nitrogen absorption and elimination rates.

When planning a dive using a dive table, divers must first determine the maximum depth and bottom time for their intended dive. They must then consult the appropriate table to identify the required decompression schedule, taking into account the breathing gas mixture used.

For multiple dives, divers must also consider the surface interval between dives and the residual nitrogen levels in their bodies. The dive table will help determine the repetitive dive group and adjust the decompression schedule accordingly.

Dive Tables and Dive Computers

While dive tables remain an essential tool for divers, the advent of dive computers has streamlined the process of calculating decompression schedules. Dive computers use real-time data and sophisticated algorithms to provide customized decompression schedules based on a diver’s actual dive profile, gas mixture, and previous dives.

Despite the convenience of dive computers, divers are still encouraged to maintain proficiency in using dive tables. Understanding dive tables helps divers appreciate the principles behind decompression planning and develop a solid foundation for safe diving practices.

Limitations and Considerations

Dive tables are designed with a conservative approach to provide a margin of safety for divers. However, they cannot account for individual physiological differences or external factors such as dehydration, fatigue, or cold

water exposure, which can influence a diver’s susceptibility to decompression sickness. Therefore, it is essential for divers to be aware of their personal limitations and environmental factors when planning a dive.

Additionally, dive tables are based on specific assumptions about a diver’s ascent rate and decompression stops. Divers must adhere to these assumptions for the tables to be effective. Any deviation from the prescribed ascent rate or decompression stops can increase the risk of decompression sickness.

Dive Table Training and Certification

Dive training organizations, such as PADI, NAUI, and SSI, incorporate dive table instruction into their certification courses. Students learn the basics of decompression theory, dive planning, and the use of dive tables to calculate decompression schedules for various dive profiles.

As divers progress through more advanced training and certification levels, they may be introduced to additional dive table systems or specialized tables for mixed gas diving. This advanced training provides divers with the knowledge and skills to manage more complex dive profiles and utilize enriched air Nitrox, Trimix, or other breathing gas mixtures safely.

Safety Precautions

Dive tables serve as a valuable tool for planning safe dives, but they should be used in conjunction with other safety practices:

1. Dive within your certification and experience level: Divers should not attempt dives that exceed their training or experience.
2. Buddy system: Diving with a buddy ensures that help is readily available in case of an emergency.
3. Monitor dive conditions: Divers should be aware of and monitor factors such as water temperature, visibility, and current, as these can influence dive safety and decompression requirements.
4. Proper equipment maintenance: Regular inspection and servicing of dive equipment are critical to ensure its reliability and safety.
5. Personal fitness: Maintaining good physical fitness and health can reduce the risk of decompression sickness and other dive-related injuries.
6. Adherence to safety guidelines: Divers should follow the guidelines and recommendations provided by their training organization and adhere to the ascent rates and decompression stops specified by the dive tables.

Conclusion

Dive tables play a crucial role in promoting safe diving practices by providing divers with the information necessary to plan and execute dives with appropriate decompression schedules. Understanding and using dive tables effectively is a fundamental skill for all divers, ensuring that they can mitigate the risk of decompression sickness and enjoy their underwater adventures safely. As diving technology advances and dive computers become more prevalent, divers must continue to appreciate the importance of dive tables and the principles of decompression planning that underpin them.